You have already answered your own question. Placing a small amount of adhesive under the body of the component, will secure it to the substrate prior to reflow and insure the X, Y and Z position does not change.
Most surface mount adhesives cure around 100 degrees c, this is just before the flux in the solder paste becomes active and well before the metal becomes liquid, insuring the component will not move during reflow.
Adding a glue machine to the line is one option, however, many placement machines today also have adhesive dispensing capabilities precisely for this reason. Machines that have dispensing options include, the Fuji NXT and Fuji XPF placement systems.
Fuji America Corporation
Scott Wischoffer has been in the SMT industry since 1986 with experience in service, training, sales & applications, and marketing.
The only way to secure them is with an adhesive. While you mention you do not have a glue machine, you can purchase a hand dispenser for SMT adhesive for well under $400.00USD. Once the parts are secured, you will be able to solder them without movement.
If you prefer not to glue them, you can hand solder them post reflow.
Regional Sales Manager
OK International Inc.
Ed Zamborsky is a Regional Sales & Technical Support Manager for Thermaltronics, located in New York. His position requires frequent customer visits throughout North America and the Caribbean and his position encompasses not only sales but the role of trainer and master applications engineer for all of Thermaltronics products. His expertise includes such specialties as hand soldering, convection and conduction reflow techniques, array rework, fluid dispensing equipment, and fume extraction. Ed has authored many articles and has presented many papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead-Free Hand Soldering, High Thermal Demand Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.